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childhood sub for living room
childhood sub for living room
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Old 4th December 2020, 09:42 AM   #1
pschach is offline pschach
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Join Date: Dec 2020
Default childhood sub for living room

Hello!

I have a 4 Ohm 12" subwoofer with 200 RMS, 40 Peak ( Rockford Fosgate P212S4 Punch Stage 2 12" 4-ohm subwoofer at Crutchfield )

from years ago and built a beautiful box for my first car out of it. Now I will be home over the holidays and would like to take it out of the attic and put it to use in our home stereo.

So far I have figured out I would be fine as long as I use an amp that can handle 4 ohms. This one even has a crossover built in ( Lepai 2.1 2x40W Amplifier LP-168HA without Power Supply )... so it seems like a good solution. Is the power going to be enough? I'd rather have an amp that can match the 200 RMS of my sub... any suggestions?

Second question is how I connect to my stereo. I could use some line level converters as I did when I had this in the car, but I think it is possible to use the TAPE OUT ? It is an old Panasonic amp from the 70s.

Thank you for the guidance. I'll be home for a month including quarantine and want to make the most of it.
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Old 5th December 2020, 01:35 AM   #2
sgrossklass is offline sgrossklass  Germany
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As little as I know about car audio, I do know that car audio subs rarely lend themselves to hi-fi use. What sort of volume is your sub? I found the following TSPs for this driver:
FS 25 Hz
Qts 0.488
VAS 97 l
Xmax 11 mm
Znom 4 ohm
86 dB / W / m
with recommended
sealed box volume: 24.07 l
vented box volume: 49.55 l
...with port D x L = 10.16 cm x 27.94 cm

Those recs must be for car audio. Entering VAS and FS into a sealed box calculator, I'm getting substantially more than 24 liters... for Q = 0.707, it's 67.8 l damped / 88 l undamped. If I'm willing to accept Q = 0.85, it's 37 / 48 l. A "small" (B4) vented box calculator gives me a 106 liter box and a 10 cm x 39.5 cm port.

The amplifier (note: external power supply still required!) seems to be using a TDA7379 chipamp:
Teardown Tuesday: Hi-Fi Audio Amplifier with Bluetooth - News
This part is specified at 2x 13 W + 1x 38 W (so 4 amplifiers total, 2x SE + 1x BTL), and I'm sure even that includes a fair bit of following wind (like 10% THD at 14.4 V) - realistically you'll be seeing more like 5 W SE / 20 W BTL for a 4 ohm load. There's only so much you can do on a max 14.4 V supply without resorting to boost converters, as better-quality car power amps do (mid-power units have an inverter to double available voltage swing at least, higher-power units feature boost converters for both rails).

I'd suggest building a new sub enclosure and buying a subwoofer plate amplifier with a decent feature set (level, crossover, phase). Having a high level (speaker level) input would seem advisable in your case, unless your trusty Panasonic amp (Panasonic, not Technics?! Was any Hi-Fi sold under this brand?) includes pre-outs - a tape-out is fixed level and thus not usable.
Properly integrating the sub and reducing the load on the main speakers may still prove difficult like this; you stand a better chance when using a computer as source and a measurement microphone. (They say when adjusting bass level by ear, the layman will get it 20 dB too high and the pro 10 dB too high still.)

If all fails there's always the $99 Monoprice sub, which probably doesn't have a driver as good as yours but is a good performer and ready to go.

Last edited by sgrossklass; 5th December 2020 at 01:39 AM.
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